1. Field of the Invention
This invention relates in general to the construction of shield devices for excavations and in particular to a new and useful shield tubbing for longwalls which includes a break shield mounted pivotally on a back filling side of a bottom tub and with at least one hydraulic ram supporting the break shield which determines the setting load and the carrying capacity of the tubbing.
2. Description of the Prior Art
In the known shield tubbings the shield bears in the range of the face of the roof with the interposition of a roof cap. The shield is supported by a longitudinally adjustable and principally hydraulically operated ram which is also supported on the ground sill. A shield tubbing frame is known which includes a shield formed by an angle lever whose lower arm acts on a piston cylinder assembly which is mounted in the ground sill along its longitudinal axis. In all shield tubbing frames according to the state of the art at least one hydraulic cylinder must transmit the entire setting load and the nominal load to the ground sill. Beyond that the cross-section of the shield must be so designed that it can absorb the load acting on it as carrier on two supports.